1. Field of the Invention
The present invention relates to an illuminating device, an image display device loaded with the illuminating device, and a mirror unit for use in the illuminating device, and in particular is preferably used in an arrangement capable of switching a light source to be used.
2. Disclosure of Related Art
Nowadays, a projection image display device (hereinafter, referred to as a “projector”) for enlarging and projecting an image onto a screen has been commercialized and widely spread. Generally, in the projector, a lamp is used as a light source, and light from the lamp is modulated by an imager for being projected onto a screen.
In use of the projector, if the lamp is short-circuited during a projection, display of an image is interrupted. To avoid such a drawback, there is proposed an arrangement of preparing two lamps in advance. If one of the lamps in use is short-circuited, the other lamp will be used.
In the above arrangement, the two lamps are disposed opposite to each other, and a mirror unit is disposed between the lamps. The mirror unit has a pivotable mirror. When a first lamp is used, the mirror is positioned to a first position facing the first lamp; and when a second lamp is used, the mirror is positioned to a second position facing the second lamp.
In the case where the lamps are switched over by using the mirror, it is necessary to tilt the mirror at a proper angle with respect to light from the corresponding lamp. Specifically, if the tilt angle of the mirror is displaced from a proper angle, unevenness of colors and deterioration of illuminance may occur in a projected image. In view of this, in the above arrangement, it is necessary to precisely position the mirror to the first position or the second position.